The UK Independence Party has made huge electoral gains and declared itself the "official opposition" - largely at the expense of the Tories - as Prime Minister David Cameron vowed to win back Conservative voters who had defected.
With UKIP averaging 26% of the vote so far in county council polls, leader Nigel Farage said he was "astonished" by the party's breakthrough, and put it down to what he described as the "total disconnect" between the "career politics" of Westminster and ordinary people on the streets.
"UKIP is actually speaking the language of millions of ordinary voters," he told Sky News' Boulton & Co programme.
Speaking in his Oxfordshire constituency, Mr Cameron said he would "work really hard" to win back voters who switched support.
The Conservative leader said all the mainstream political parties had "major lessons" to learn.
David Cameron has pledged to win back voters who switched support to UKIP
"For the Conservatives I understand why some people who have supported us before didn't support us again, they want us to do even more to work for hard-working people to sort out the issues they care about," he said.
"More to help with the cost of living, more to turn the economy round, more to get immigration down, to sort out the welfare system. They will be our focus, they are our focus, but we have got to do more."
Asked if he stood by his "fruitcakes" attack on UKIP, Mr Cameron said: "Well, look, it is no good insulting a political party that people have chosen to vote for. Of course they should be subject and they will be subject to proper scrutiny of their policies and their plans.
"But we need to show respect for people who have taken the choice to support this party and we are going to work really hard to win them back," he added.
UKIP became the second largest party in Lincolnshire as the Conservatives lost control of that county council as well as Gloucestershire - and also reduced the Tories' grip on power in Essex and Hampshire.
Mr Farage drinks a pint at the Marquis of Granby in Westminster
The eurosceptic party also finished second with 24% of the vote behind Labour in the South Shields parliamentary by-election, triggered by the resignation of David Miliband, with the two coalition parties suffering a drubbing.
The new MP, Emma Lewell-Buck said her victory was a verdict on the Government's austerity measures.
It was another bad result for the Conservatives who finished third, and a disastrous one for the Liberal Democrats who lost their deposit and finished seventh with just 352 votes behind UKIP, the Tories, an independent, the Socialist Party and the BNP.
"Send in the clowns," said a jubilant Mr Farage, after UKIP candidates were famously dismissed by Mr Cameron as "fruitcakes, loonies and closet racists" and last week as a bunch of "clowns" by Tory Cabinet minister Ken Clarke.
"We've been abused by everybody, attacked by the entire establishment who did their best to stop ordinary decent people going out and voting UKIP, and they have done in big, big numbers," he told Sky News.
"By the end of today we are going to have a fair tally - and it sends a shock wave, I think, through the establishment."
Asked whether UKIP were no more than the beneficiaries of protest votes against the coalition Government, Mr Farage replied: "If you speak to the Westminster elite, they will tell you 'it is just a protest, nothing to worry about really'.
Labour's newest MP Emma Lewell-Buck wins the South Shields by-election
"When I meet UKIP voters they say, 'Nigel, we're voting for you because we believe in what you stand for'.
"These votes are not easily going to go back to the Labour and Conservative parties."
Senior politicians from the three main parties attempted to explain the UKIP surge, which could have major implications, particularly for David Cameron as he attempts to calm the fears of grassroots Tories nervous at the loss of votes to Mr Farage's party.
UKIP's success will heighten pressure on Mr Cameron to shore up right-wing support by legislating during this parliament for a referendum on EU membership.
Conservative Chairman Grant Shapps acknowledged that his party had been hit by the rise of UKIP.
He told Sky News: "We hear the message, we get it, we understand what people are saying. They want to see change faster in this country and that is what we intend to deliver over the next couple of years.
"We need to show that we are relentlessly on the side of hard-working people in this country, who want to get on in life, do the right thing, and Conservatives back them.
"We have actually been making progress - we've cut the deficit by a third and cut net immigration by a third.
Richard Elvin, the UKIP candidate who came second in South Shields
"My main concern is to listen to the voters and make sure we are reflecting their concerns - putting jobs and prosperity and fixing the economy first and foremost - that's where all our time and energy is going to be focused."
But the Tory grassroots and backbenchers were seething at the party's performance.
Conservative Party vice-chairman Michael Fabricant tweeted "life cannot go on as normal" for the main three parties "unless they have no ambition for 2015".
One defeated Tory councillor in Hampshire launched a scathing attack on Mr Cameron, saying: "I don't believe a word he says."
Alexis McEvoy lost her South Waterside seat to UKIP's Philip Fawkes - a retired headteacher and distant relation of gunpowder plotter Guy Fawkes, who won with a majority of 315 and a 37.2% share of the vote.
Mr Farage said the win showed "the blood of rebellion still runs in his veins".
Business Secretary Vince Cable conceded the results were "obviously very disappointing" for the Liberal Democrats.
He said voters had turned to UKIP as a protest over poor economic conditions and claimed the results emphasised problems in the Conservative party.
More than 2,300 seats are being contested in polls for 34 English councils
"Unfortunately this is part of the price you pay for being in government and I think the Conservatives have had an even worse night than we did, but, nonetheless, it's not great," he told Sky News.
In East Sussex, where Labour made gains, party leader Ed Miliband said: "I'm pleased with the gains that we made in Hastings and across the South, and indeed in other parts of the country, including Derbyshire and elsewhere."
Asked whether he was worried about the threat of UKIP, he replied: "Part of Labour's challenge at the next election campaign is not the Tories, or the Lib Dems or even UKIP, it's the idea that nobody can really change the country, and that mainstream parties can't change the country.
"I believe Labour can change the country. I believe we have convinced a lot of that in these elections and that's why we have made a lot of gains, but I also know that there's work to do that goes on."
Liberal Democrat leader Nick Clegg conceded that results for his party, which lost around a quarter of its councillors, were "not good".
He said: "I have always said it is understandable why it is that people might be attracted to the simple answers that the UK Independence Party is offering to deal with this country's complex problems.
"But I do not think they do have the answers to the dilemmas we face as a country.
Ed Miliband speaks to voters in Hastings, East Sussex
"Of course, it is not good to lose half your councillors, as we have done in these elections, but the Liberal Democrats are on a journey.
"We are on a journey from a party of protest to a party of Government and actually the pattern that has emerged from the results overnight shows that, where we have MPs, where we have Liberal Democrats out on the doorstep setting out our side to the story, communicating our message, we are holding our own and in some areas making gains."
The Conservatives retained control in Buckinghamshire, Devon, Dorset, Essex, Hampshire, Hertfordshire, Kent, Shropshire, Staffordshire, Suffolk, Surrey, Leicestershire, North Yorkshire, Northamptonshire, Wiltshire, West Sussex, Worcestershire and - narrowly - Somerset, where they lost five seats and the Liberal Democrats lost four.
But they were ousted from overall control in Cambridgeshire, Gloucestershire, Lancashire, Warwickshire, Lincolnshire, Norfolk Oxfordshire, Nottinghamshire, Isle of Wight and East Sussex.
The Tories were sent a warning in their traditional Essex heartland, losing nine county council seats to a bullish UKIP.
And they were held to "Ransome" in Lincolnshire as mother-of-four Sue Ransome and her daughters Felicity and Elizabeth celebrated three UKIP gains in Boston.
Sushil Kantibhai Patel, the father of Tory MP Priti Patel - took second place behind the Conservatives as the UKIP candidate in the Bushey South ward in the Hertfordshire County poll.
There was some good news for Nick Clegg as the Lib Dems won the by-election in the Fulwood ward in the heart of his Sheffield Hallam constituency in South Yorkshire, ahead of Labour, the Tories and UKIP.
Labour gained Derbyshire County Council from no overall control - and won the mayor battle of North Tyneside with the party's Norma Redfearn ousting incumbent Tory Linda Arkley.
The BNP lost its only county council seat in Padiham and Burnley West in Lancashire.